An analysis of a mutant mouse, "EYELESS" will be performed. This is a powerful model for developmental studies of the visual pathways. In this mutant, a sequential series of developmental arrests and/or repressions take place in defined stages, and it can be expected that it will be possible to determine whether ultrastructural changes of the occipital cortex result from the absence of a functional visual input. The mouse model is particularly interesting because of the recorded existence of a similar genetic anomaly in man. The eyeless mouse provides a key to the human nervous system which otherwise is unapproachable experimentally. I plan to analyze the role which the primary projections (absent in this mutant) play in the development of visual cortical elements, and to characterize the organization of cortical "columns" in normal and abnormal conditions. Human specimens will be available through the Neuropathology Department and affiliated hospitals, and an analysis will be made of these brains. Regional specificity will be pursued through reconstructions at the level of the electron microscope and the visual cortical fine structure will be examined in terms of its architecture, components, and especially its synaptic arrangement. Experimental surgical procedures will be performed and a thorough statistical analysis of the results will be made.